Topic: tire pressure with nitrogen

[CaldwellB]

A silly question this may seem - should a tire inflated with nitrogen be inflated at the same pressure as it if it was inflated with air?  I'm aware that air is 78% nitrogen so it would seem the answer would be yes.

I ask as I had new tires installed at Costco (filled with nitrogen) two weeks ago and checked the pressure tonight (for the first time since installation) and they're all at 20 psi (should be 30).  If anything I would have thought they would have been ~34 (like my other car with air in the tires) with the warm weather this past week.   I would have thought that the mileage would have suffered as well, but oddly it hasn't...

-Barry

[UmroAyyar]

There have been quite a few discussions about nitrogen's use in tires.

Here are a few links to those discussions.

http://www.canadiandriver.com/forum/index.php/topic,54835.0.html

http://www.canadiandriver.com/forum/index.php/topic,46093.0.html

http://www.canadiandriver.com/forum/index.php/topic,53495.0.html

Regarding air pressure, I check the tires immediately after service at the dealer or tire repair/rotation/installation at the tire shop. More often than not, the pressure is not correct. 20psi instead of 30psi might not damage the tire quickly enough.

[dorin]

Depends, are you using Hercules G5000Z 215/40RZ17 tires! 











Sorry, that's just a running joke.  Regardless of what you're using to inflate your tires you don't want them at 20 psi, so nitrogen or regular air make sure your tires are at least at the recommended tire pressure.

[xviper]

The answer would be "yes".  XX psi of air is the same as XX psi of N2.  It might take a slightly different quantity (in terms of "moles") of one over the other to exert the same pressure, but it would be the SAME pressure.
Always check tire pressures after any work has been done to them.  Best to rely on the cold pressure check first thing in the morning.
Each type of car has its own recommended tire pressure.  What your "last" car used for tire pressure doesn't relate to what your present car should have.

[capriracer]

Barry,

If all 4 tires are about the same, then either your gauge is off, or they didn't fill the tires enough.  In either case go back and see if you can discover which problem it is.

[morty]

Capriracer is correct. The chances of all 4 tires losing exactly the same amount of pressure is very minimal. Just go back to Costco and have them check the pressure. If there is a problem they will fix it. If not, you will know your gauge is defunct.

[safristi]

... why would i want Moles in my tyres..........N2Yaah N2YAAH nana N2Yah!!!

[xviper]

... why would i want Moles in my tyres..........N2Yaah N2YAAH nana N2Yah!!!

Had I used hampsters the gay audience may have objected.   

[je]

I read in a scientific study that oxygen is 3-4 times more permeable through butylene rubber than nitrogen. I still don't think even that is significant. Interestingly, CO2, which is a much larger molecule, is significantly (ie order of magnitude, even 15 times) more permeable due to its solubility in the rubber - or else it would be a great inflator (does that contradict my earlier statement?)

Tell me, is the permeability significant?
What's the leak rate through the rubber, compared to leaks around the bead, the valve, or the valve core? 

[CaldwellB]

Apparently it's my pressure gauge, I went back to costco and the pressure was fine.  My gauge measures the pressure correctly with air but not nitrogen.  Where can one buy a pressure gauge to measure nitrogen?

[xviper]

Odd.  I would not have thought that it would make any difference.  Is there even such a thing as a N2 pressure gauge?  What did Costco use?  I doubt they used such a device.  Maybe your gauge is just forked.

[tpl]

Sounds very unlikely.  The gauge is a simple device that doesn't care what it measures... it just measures the distortion of something caused by a pressure  differential.

After all   Air is 78% nitrogen.

[HeliDriver]

Apparently it's my pressure gauge, I went back to costco and the pressure was fine.  My gauge measures the pressure correctly with air but not nitrogen.  Where can one buy a pressure gauge to measure nitrogen?

Are you using one of those slider-type gauges? If so, I doubt it's measuring anything correctly. Those things are famously unreliable.

You can spend a bunch of money on a nice dial-type pressure gauge, but I've also had pretty good luck with the $10-15 digital gauges.

[CaldwellB]

I have a dial-type gauge.  It measures my other car's tires(filler with air) correctly.  Costco didn't use a gauge, they just enter the req'd pressure and it beeps when it's set.

[tpl]

Then I wouldn't trust the Costco device.   

[xviper]

It measures my other car's tires(filler with air) correctly.  Costco didn't use a gauge, they just enter the req'd pressure and it beeps when it's set.

If it works correctly on another car, then it should work on N2 filled tires.  If those tires are indeed at 20 psi and you have some sort of car experience, the there's a simple test.  A car with 20 psi in the tires, compared to a car with 30+ psi in the tires will react very differently.  Push the top of any tire in and out (from the car) and see how much flex movement there is.  The 20 psi car will have a lot of movement while the 30 psi car will have much less.  Similarly, if you have a good feel for how the car rides, the 20 psi car will feel "spongy" compared to the other car.  Many people can tell by just looking at the sidewall and know if it's down 10 psi or more.

Then I wouldn't trust the Costco device.   

Precisely!

[tpl]

As for digital tire pressure gauges.
I have a small electrical tire pump from Cdn tire. Works well on its own battery or plugged into the cigar lighter.
It can turn off automatically at a preset pressure.  Works well.
It can display pressures in psi, bar or Kpa(Newtons)   also good.

BUT the psi/kpa/bar indicator on its tiny display is very small indeed.

I was pumping up my summer tires when I installed them and after the pump had been running on one tire for about 5 minutes and was getting warm I checked.  It was trying to pump the tire up to 32 BAR... unsuccessfully fortunately but it had got to nearly 50 psi which is a bit above the limit for my tire.  The pump is not clever enough to convert so that when I'd selected 32 psi and inadvertently selected bar to set itself to turn off at 2.26. 

SO I wonder if Costco had some weird thing on their pump/gauge.


I have my own pump 'cos I have never found a garage pressure gauge I can trust.   However when the Fits winter tires arrived from Tire trends they were all spot on 32psi according to both my gauges. ( 32 psi is correct for the Fit)

[mrthompson]

I have two slider type gauges....one for each vehicle.  There is a 1-2 psi difference between the two gauges.  What is the consensus regarding digital gauges?  There's one on sale at CT this week for $9.99.

[xviper]

I've always liked the digital air gauges, but I've also used the dial type ones, too.  They both work well.  Now that I have my own air tank in my garage, I use an "air gun" to fill my tires and there's a built in dial type pressure gauge on it.  It's within 1 psi of my digital gauges.  Makes for easy work when the filling device and measuring device is on one thing.

PS.  I've always questioned the value and extra cost of using N2 in a daily driven car.  The benefits and stability of that last 20% of N2 won't be felt unless you are running on a track circuit.  I think the N2 sellers have done some brainwash marketing.